1. Field of the Invention
The present invention relates to an apparatus for regenerating a particulate filter for collecting particulate matter contained in exhaust gas from an engine.
2. Description of Related Art
Exhaust gas discharged from an internal combustion engine, a diesel engine for example, contains particulate matter (may be referred to as “PM” hereinafter) such as soluble organic matter and soot. Accordingly, it is common to provide a vehicle with a particulate filter to collect PM to clean the exhaust gas, and burn off the collected PM to regenerate the particulate filter.
It is known, as a method of regenerating a particulate filter, to cause an injector provided in an exhaust pipe of an engine (referred to as “exhaust pipe injector” hereinafter) to inject fuel into the exhaust pipe in order to raise the temperature of the exhaust gas utilizing the oxidation reaction heat generated by the oxidation reaction between the injected fuel and a diesel oxidation catalyst (may be referred to as “DOC” hereinafter), to thereby heat and burn off particulate matter collected in the particulate filter. For more details, refer to Japanese Patent Application Laid-open No. 9-222009.
The exhaust pipe injector is configured to open when an actuator thereof such as a solenoid is energized. It is also known that an apparatus for regenerating a particulate filter is provided with a function of performing fault diagnosis on the drive system of an exhaust pipe injector by causing a driver circuit of the drive system to actually energize an actuator of the exhaust pipe injector, and judges whether the drive system is functioning normally by monitoring the energization state of the actuator. Such a fault diagnosis is performed when the exhaust pipe injector is driven to regenerate the particulate filter.
However, since the regeneration of the particulate filter is performed with frequency as low as once per several thousand kilometers traveled by the vehicle, the frequency of performing the fault diagnosis is also low, which causes delay between occurrence of a fault and detection of the fault. It is common that only after a fault is detected a predetermined number of times, a determination of presence of the fault is made. Accordingly, in this case, the time between occurrence of a fault in the drive system of the exhaust pipe injector and determination of presence of the fault is further lengthened.
In addition, the period of time during which the exhaust pipe injector is driven to regenerate the particulate filter is not always constant. When the exhaust pipe injector is driven for only a short period of time, it may not be possible to accurately perform the fault diagnosis.
Furthermore, in a configuration where the exhaust pipe injector is forcibly driven by a request command from an external fault diagnosis apparatus, it is not preferable to forcibly drive the exhaust pipe injector at arbitrary times in view of the efficiency of regeneration of the particulate filter and engine control, because it needs to inject extra fuel into the exhaust pipe.